fix(cpp-qt): Fix enum query parameter serialization for both inline and referenced enums

[ReallyVirtual]

Fixes enum query parameter serialization for cpp-qt-client generator.

Problem

For enum query parameters, the template was incorrectly using asJsonObject() which returns {"value": "enumValue"} and then iterating over keys, using "value" as the parameter name instead of the actual parameter name.

This resulted in incorrect URLs like: ?value=property instead of ?scope=property

Solution

Added special handling for both inline enums (isEnum) and referenced enums (isEnumRef) in the api-body.mustache template to use asJson() directly, which returns the correct enum string value for URL serialization.

Changes

Modified modules/openapi-generator/src/main/resources/cpp-qt-client/api-body.mustache to detect both enum types and use direct string serialization
Updated cpp-qt-client samples (though petstore samples don't contain enum query parameter tests to demonstrate this specific fix)
Context
Completes the fix started in PR #21211 which added the asJsonObject() method to make enum code compile, but the template logic was still incorrect for URL query parameter serialization.

Testing

✅ Built OpenAPI Generator successfully
✅ Generated cpp-qt-client samples without errors
✅ Verified enum parameters now serialize correctly in generated code

Note

The petstore samples don't contain enum query parameter examples to showcase this functionality. Future contributors may want to add enum query parameter tests to better demonstrate this fix.

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[wing328]

thanks for the PR

what about adding some fake endpoints to modules/openapi-generator/src/test/resources/3_0/cpp-qt/petstore.yaml to cover this change?

for example https://github.com/OpenAPITools/openapi-generator/blob/master/modules/openapi-generator/src/test/resources/3_0/petstore-with-fake-endpoints-models-for-testing.yaml#L1280-L1305

[ReallyVirtual]

@wing328 Sure. I'm using my fork with the change to generate usable code for enums (that doesn't require a .value), and will add something similar to my use case next weekend.